Saturday, October 31, 2015

Our field studies trip to Yosemite National Park reached a climax when we reached Tioga Pass (9,943 ft / 3,031 m) at the east end of the park. The pass is the highest highway route in the state (a paved road in the White Mountains and the Bristlecone Forest reaches just a few feet higher, at 10,075 feet). The scenery at this elevation is spectacular. The surrounding peaks reach over 13,000 feet (nearly 4,000 meters), and glaciers have scoured much of the terrain to barren rock. Few trees can survive in this harsh environment.

There is not much in the way of granite east of the pass. The white expanse of plutonic rock in Tuolumne Meadows has given way to older, darker rocks that began their existence as volcanic rocks and oceanic sediments more than 200 million years ago. They have been baked and deformed by deep burial in the crust. There is also the remains of a caldera, a giant collapse depression similar to the one that formed Yellowstone or Long Valley, but in this instance we are seeing it from the base, the part that was once a mile or two underground..

This was the source region for the glaciers that scoured the Grand Canyon of the Tuolumne and Yosemite Valley. Numerous cirques, horns and aretes can be seen along the Kuna Crest and the main Sierra Crest. There are even a few small glaciers tucked into the high canyons (Dana Glacier is accessible by trail).

It was the end of our field studies course, and I fervently hope that it will be the last chance of seeing Tioga Pass. For a while anyway. I had the fascinating but unfortunate privilege of seeing Tioga Pass on an early January day in 2012, because there had been no snow. It was strange walking across a solidly frozen Tenaya Lake (visible in the top picture) in a t-shirt and jeans when there should have been 10-15 feet of snow everywhere. We've had a disastrous run the last four years with an unprecedented drought, the worst in many generations, even centuries. There is hope that El Nino conditions in the Pacific Ocean will bring on more than the normal amount of rain and snow, but that remains to be seen. There have been a few weak storms already, and another system coming in Monday. Some hopefully fortunate events, as it were.

As beautiful as it is, I hope I won't have another chance to see Tioga Pass until May at the earliest.

Thursday, October 29, 2015

There are domes and there are "domes". Yosemite National Park has a lot of domes of one sort or another, and there has always been a bit of confusion about their origin. From various points in Yosemite Valley, one can spy at least four them, famous Half Dome, less famous Sentinel Dome, North Dome, and Basket Dome. Although Yosemite is famous as a work of glacial action, the domes actually are not directly related to glacial erosion. As described in the previous post on Sentinel, these domes rose above the glacial ice. They formed instead because of exfoliation, the tendency of slabs of granitic rock to break off the corners and edges of monolithic chunks of exposed rock. In time they take their rounded shape.

Image from http://villains.wikia.com/wiki/Monstro

In the high alpine parts of Yosemite, the situation is different.
Tuolumne Meadows is not a "U"-shaped glacial valley. It has an open
aspect, with high mountain ridges separated by wide meadowlands dotted
with granite monoliths that rise above the dark forests. The granitic knobs look less
like rounded domes, and more like Monstro the Whale breaching at sea,
with a gentle slope on one side, and nearly vertical cliffs on the
other. Two of the most obvious are Lembert and Pothole Domes. Both rocks are popular hiking destinations, and both provide stunning views of the high country of Yosemite. Pothole Dome was our destination on this trip.

The open country of Tuolumne Meadows resulted from a different kind of glaciation. In Yosemite Valley, the glaciers only occupied the valley itself. At Tuolumne, the glaciers covered the entire landscape apart from the highest peaks. The depth of the ice exceeded 2,000 feet (~700 meters). Such glaciers are called icecaps or icefields, and they produce a different set of erosional features. Pothole and Lembert Domes are examples of Rock Mutton.

Oh, excuse my French! The domes are examples of a roche moutonnée. This has been translated variably as greasy mutton wig rocks, fleecy rock, or rock sheep, and none of these is a particularly apt description. The first was related to the sheep grease that was used to hold the hair in place in the old wigs worn by French and English dignitaries. The fleece referred to the "resemblance" of these rocks to the locks of hair in the aforementioned wigs, and the last was said to be a description of the rocks appearing as grazing sheep from distant vistas. I don't quite get it, but c'est la vie.

Whatever you might want to call it, Pothole Dome provides an intimate
understanding of what rock is like when subjected to intense glaciation. The gentle slope, which faced the oncoming ice flows, has been smoothed and abraded by rocks, sand, silt embedded in the ice. The passage of the gritty ice has left grooves, striations, and polished surfaces that make climbing the dome a great deal easier than one might expect. Most of the huffing and puffing comes from the high altitude (8,000 feet/~2,700 meters) rather than steepness.

The steeper western side of Pothole Dome was "plucked". Ice formed in cracks and fissures of the granitic rock and was pulled loose by the glacier as it flowed away from the rock. This made for a decidedly asymmetrical dome structure if one wants to call it a dome at all.

An alternate term for these rocks is a stoss and lee structure. "Stoss" comes from a German term for "push" or "thrust", referring to the gentle slope facing the flow of ice (the glacier "pushes" up the slope). The "lee" refers to the trailing steeper plucked side. I tend to prefer this description, although it still isn't all that descriptive. How about a "scour and pluck" structure?

The other unmistakable evidence of the passage of glaciers is the sheer numbers of boulders that lie scattered across the surface of the dome. There aren't many good explanations for how these boulders could have gotten here without invoking the passage of ice (the boulders came from a different kind of granite exposed off to the east). These out of place rocks are called glacial erratics.

There are marvelous examples of glacial polish and striations all over the surface of Pothole Dome. The ice was last here around 12,000 years ago, so the rough surfaces surrounding the polished sections provide an idea of how slowly the granite is weathered in this cold alpine climate. At lower elevations, the rock would weather much faster and the polish would rapidly disappear.

From the top of the dome, one can see some of the terrain that stuck out above the icecap, including the Cathedral Range (below). The peaks are classed as horns when glaciers flowed away from the mountain, plucking away at the flanks, or nunateks when the glaciers flowed around the peaks, scouring away at the higher slopes.

Pothole Dome's name reflects the presence of potholes on the south flank of the dome. These round holes formed when ice melted into the glacier through holes and tubes called moulins. The water flowing under the ice mixed with boulders and gravel in large swirling masses to grind out the holes.

The final glacial feature we noticed while climbing down were the chattermarks, concentric fractures caused when boulders being dragged at the base of the glacier skipped and chipped the surface. Usually the cusps of the crescents point away from the ice flow direction, so I found these a bit mysterious. The crescents open toward the east, presumably the direction the ice came from.

The day was passing and we had a few stops left on the itinerary. They'll be covered next time!

Sunday, October 25, 2015

Imagine standing at one of the most famous park viewpoints in the world. Ask people standing in that place, the Wawona Tunnel Overlook at Yosemite National Park, how many granite domes they see, they might say just one. If they're feeling humorous, they might even say not just one, but half of one (let's discuss that point). But there are actually two of them. Sentinel Dome is the other somewhat less prominent dome, off to the right of Half Dome (see above).

The hike to the summit of Half Dome is the stuff of legend. One must start very early in the day, hike seven or so miles to the summit pitch (climbing 4,000 feet in the process), and then trudge up a terrifying set of cables and steps on an impossibly steep flank of the dome. People have even fallen off the trail to their deaths. I've not yet had the privilege (of hiking, not falling), but hope springs eternal!

Sentinel Dome is also climbable, but it is not nearly as taxing to the body and soul. It's only a few hundred feet shorter than Half Dome in elevation, but it is also close to the Glacier Point Road, so hiking to the summit is more of a short stroll than an all-day expedition. And it has a marvelous perspective on Yosemite Valley and the surrounding territory.

The official trail starts at the parking lot for Taft Point and Sentinel Dome trails. Get there early in the day because the parking lot fills quickly. These are popular trails. The hike to Sentinel is a mile, but if you are good with topographic maps, you can find an alternate route that is only half as long, and the parking area for the alternate way is almost always empty.

Which ever way you go, the trail passes through an open forest of Ponderosa and fir trees. As you near the ridge top, the sky opens wide and one can sense the huge chasm that lies beyond.

The summit area of Sentinel Dome is relatively barren of vegetation, and is instead an island of granitic rock rising out of the forest. The dome was not formed by the shaping effect of glaciation, and indeed glaciers never covered the summit. The rounding occurred because of exfoliation, the tendency of slabs of granite to break off of edges and corners. Walking the summit pitch one steps over the slabs like a stairway (below).

Exfoliation slabs on the summit pitch of Sentinel Dome

The exfoliation occurs because the granitic rock forms by the slow, slow cooling of silica-rich magma deep in the Earth's crust. The rock expands as it is exposed by erosion near the surface and fractures outward. The process still occurs in the region today. I've witnessed rockfalls from this very spot (see here for the story), and I posted last year about an exfoliation event in Twain Harte.

The view from the summit of Sentinel Dome is nothing short of spectacular. The Cathedral Rocks and El Capitan dominate the view west, while the Sierra Nevada foothills slope away in the distance towards the Great Valley.

East and south, the view takes in the high peaks of the Sierra Nevada Crest and the Clark Range.

Half Dome and Cloud's Rest dominate the scene to the east. Tenaya Canyon and Little Yosemite Valley lie in the shadows below. Yosemite Falls, had it been flowing, would have been visible to the north.

There used to be an iconic tree, a windblown Ponderosa Jeffrey Pine, at the summit. It appeared in many National Park Service photos. A vandal girdled the tree with a knife, killing it. Even here, people can be jerks and worse.

I took a 360 degree panorama with my video camera. It's linked below if you'd like to take a look!

We hiked back down to the cars and drove to the valley floor. The class was about the geology of Yosemite National Park, which encompasses over a thousand square miles. Yosemite Valley covers only about seven square miles, so we spent a surprisingly short period of time down there. We were headed for the high country, which we'll cover the in the next post!

This might be of interest only to my Modesto area readers, but anyone who is interested in learning about the natural and human history of the Hawaiian Islands may want to investigate this field studies opportunity June 1-13, 2016. I am collaborating with anthropologist Dr. Susan Kerr of Modesto Junior College to guide students on an exploration of two of the most fascinating islands in the Pacific Ocean, Hawai'i (the Big Island), and Kaua'i.

The islands are an outstanding outdoor laboratory for understanding basaltic volcanism associated with a "hot spot", or mantle plume. The Big Island consists of five overlapping shield volcanoes, including the largest and highest mountains on the planet, Mauna Loa and Mauna Kea. Measured from their base on the ocean floor, the volcanoes are more than 30,000 feet tall. The portion that rises above sea level is impressive. It is possible to collect snow from the summits during part of the year. Glaciers once collected on the summit of Mauna Kea!

Although we couldn't possibly guarantee lava on our trip, Kilauea has been producing lava flows nonstop for more than thirty years. Subsurface activity has been noted for the last few weeks at Mauna Loa. It hasn't erupted since 1984, but who knows?

Of course, volcanism is hardly the only fascinating topic of study in the Hawaiian Islands. There are tropical jungles and deserts is well as the iconic beaches (including a green sand beach, the sand grains composed of the mineral olivine!). There are striking examples of evolution in action, with highly adapted plant and animals species, including a group of native Honeycreepers that are (or were) as diverse as Darwin's finches on the Galapagos Islands. There are even native owls, hawks, and geese (the Nene is the state bird; some Canada Geese made a wrong turn a half million years ago).

The human story is no less compelling, from the arrival of Polynesians hundreds of years ago to the later mingling of cultures that make the state one of the most diverse human communities on the planet.

We will spend about nine days on the Big Island, working out of hotels in Hilo and Kona. We'll then fly to Kaua'i to spend four days exploring the small, older island, including overlooks of the legendary Na Pali Coast, and the "Grand Canyon of the Pacific", the incredible Waimea Canyon. Although the itinerary is ambitious, we will work time in for some optional personal explorations, including possible hikes into Waimea Canyon, or onto the Alaka'i Swamp, one of the strangest environments on the planet (the swamps receive hundreds of inches of rain every year).

The cost of the classes will be $2,200 for lodging, transportation, and fees. Participants will need to pay their fare to and from the islands, and provide their own food (the fee includes the inter-island flight). The students will enroll in Geology 190 and Anthropology 190 (through Modesto Junior College). There are no prerequisites, although previous courses in geology or anthropology certainly wouldn't hurt. The tuition will be about $300 (unfortunately the out-of-state tuition is considerably higher)..

We are having an organizational meeting on Friday, October 30 on the West Campus of Modesto Junior College at 7PM in Science Community Center Room 326. Attendance is not mandatory and brochures will be available for those who can't make it. Initial deposits will be due in mid-November, and priority space will be given to the first twenty students who commit to the trip. If there are more than twenty, we will try to accommodate them if possible.

Friday, October 23, 2015

Glacier Point on the rim of Yosemite Valley is hands-down one of the most spectacular places one can stand in the world. There's just no place like it. And it's noisy. It's crowded. There is a busy and often full parking lot. And despite that, it is worth putting up with, because there just aren't that many places where you can look straight down for 3,000 feet, and at the same time see the iconic rocks of the upper valley from a unique angle.

It takes a little effort to get there. One has to drive about 25 miles from the floor of Yosemite Valley up a narrow winding road. One has to wade through the crowds to get the edge of the precipice. But no matter how many times I've stood there, I can never fail to be in awe that such places exist. In one sweeping view one can see the north valley wall from the vicinity of the Three Brothers and Yosemite Falls, past Yosemite Point, on to North Dome and Basket Dome, across the deep trough of Tenaya Canyon to Half Dome. And below your feet there is the floor of Yosemite Valley, the meadows, the forests, the parking areas, the resorts, all from a nearly vertical perch at 3,200 feet (980 m).

It's from a high point like this one that I can best appreciate the work of the glaciers that altered a narrow river-carved canyon into the wide, flat floor we see today. The earliest glaciers filled the valley to the rim (the Pre-Tahoe stage around 800,000 years ago), while the later advances only filled the valley to one-third or so of the total depth (the Tahoe stage at 130,000-65,000 years, and the Tioga stage from 20,000 to 13,000 years ago). The domes, like North Dome, Basket Dome and Half Dome, rose above the ice at all times. Their rounded shapes are the result of exfoliation, the tendency of slabs to break off the edges and corners of solid monoliths of granitic rock as erosion took weight off the surface of the rock. Glaciers helped excavate the rock from the jointed face of Half Dome, but never overtopped the gigantic rock.

One might think that a view like this is unchanging on a human time scale, but that's not exactly true. It's a little tricky to see it in the shadows, but look at the whitish exposure of granite to the left of Half Dome in the picture above. That scar didn't exist prior to 2009. Every visitor prior to March of that year saw something different. The Ahwiyah slide involved thousands of tons of rock that fell 1,800 feet to the floor of Tenaya Canyon. The resulting explosion of rock destroyed hundreds of trees on the valley floor. To see some before and after pictures, click here for a look.

Our class finished at Glacier Point and headed back the vehicles, but we weren't done with standing in dramatic places. That will be in the next post!

Tuesday, October 20, 2015

We spent three days exploring the geology of the Yosemite region last week, and the first stop on Saturday was Washburn Point, an amazingly quiet viewpoint given its proximity to Glacier Point. It's a parking lot, sure, but no bathrooms, no curio or snack shops, few interpretive signs, and in my experience it is far less crowded. One can't see as much of Yosemite Valley from the point as one can from Glacier, but it provides an outstanding vista of the high peaks above the valley floor. And it provides an educational peek at Half Dome. And like no other point in the valley, it reveals the lie in the dome's name. It's not a "half". At best, one could call it Three-quarters Dome, or Four-fifths Dome, but not Half Dome.

We bloggers have our favorite posts, and one of mine is the one I wrote last year as part of my "If These Cliffs Could Talk" series:Tis-sa-ack and Tu-tok-a-nu-la (A Geologic Love Story). You can click on the title to read it if you missed it originally. In the story we find that the dome is named "Tis-sa'-ack" after a beautiful stranger who disappeared after spurning the love of a chief. The chief's actions led to disaster for his people, but eventually the gods relented and the people of the valley once again had plenty

I stuck the statement way at the end of that post, but I wondered at the time why we haven't renamed Half Dome? "Tis-sa'-ack" evokes great beauty and grandeur, and recalls the culture of the original inhabitants of the valley. What does "Half Dome" evoke?

What do you think? Our nation's highest mountain now carries the original name of Denali, instead of the name of an obscure American president who never even visited Alaska. Why can't we consider the same for one of the most famous icons of one of our most beautiful national parks?

Not much can kill them. And once they've been killed, it takes a long time for them to go away. There's one in the picture above, can you see it? No, this isn't a post about zombies, it's a story about Giant Sequoia trees (Sequoiadendron gigantea), a tree with a geologic story. The dead tree in the picture above fell several hundred years ago! Despite the high level of precipitation in this forest environment, the wood is practically indestructible.

Two weeks ago we took a walk through Nelder Sequoia Grove, a collection of about 100 mature Sequoia trees just south of Yosemite National Park. I was investigating the grove as an alternative stop on our geology field studies trip last weekend, and it was a bit gloomy that day in the forest. It was actually snowing in the high country, and we worried a little about getting rained on. And the fact that the grove had been logged added a bit to the oppressive feeling of the day.

We arrived a week later, and it was a totally different feeling in the grove. The sun was shining, and the forest was serene rather than gloomy. A grove of Giant Sequoia trees is never a bunch of trees. It's a land of giants with little trees in between.

It's true that 277 of the trees that once lived here fell to the logger's saw, but 100 of them live on, and there are some young trees that will eventually replace those that were lost. Threats still exist of a different kind, threats that we all face. Global warming is changing the climate conditions in the groves, with hotter summers and thinner winter snowpacks. On the day we visited, the trees exuded a sense of permanence, sort of a feeling that they've faced challenges in the past, and they've survived. They'll survive this too, but maybe with a little help from us.

Species related to the Sequoia once existed across the northern hemisphere, The Coast Redwoods of northern California are related, as is the rare Dawn Redwood of China (discovered in the 1940s in a single grove, they are now grown as ornamentals worldwide). Climate change, including the ice ages, probably led to their extinction in most parts of the world. The Sierra Nevada is a tilted block of granitic rock, and the trees survived the drastic climate changes by propagating up and down the slopes of the range. They exist today in 68 or so groves, mostly in the southern Sierra Nevada near Sequoia and Kings Canyon National Parks. There are only four small groves in or near Yosemite National Park, including Nelder Grove, just south of the park boundary. Just three groves exist to the north of Yosemite, at Calaveras Big Trees State Park, and as a small grove of six mature trees in Plumas County.

From the Save the Redwoods League

The Sequoia trees of Nelder Grove are kind of scattered, but a visit to the grove is an exercise in solitude. It's a powerful contrast to the crowded trails of Mariposa Grove and the other groves in Yosemite National Park (Mariposa Grove is presently closed as the park service works to reconfigure visitor access to the trees, in a matter that will be more wilderness-like). If you have the time to follow the winding 9 miles of road (two miles are gravel, but accessible to normal cars), it is well worth a visit.

Sunday, October 18, 2015

The value of a river can be measured in so many ways, and the Tuolumne River here in California is no exception. It has headwaters in the spectacular high country of Yosemite National Park, flows through a gorge as deep as the Grand Canyon, gets trapped for a time in Hetch Hetchy Reservoir, and later in Don Pedro Reservoir. Then the river sort of falls out of public perception. It drains onto the floor of the Great Valley at Waterford, sort of sneaks past the city of Modesto, and joins with the very shrunken San Joaquin River before flowing into the Sacramento-San Joaquin Delta, and then into San Francisco Bay.

But what are the most important parts of a river? The scenery of the Grand Canyon of the Tuolumne and Tuolumne Meadows is unmatched, one of the most beautiful places in the world. But farmers and city planners could care less about the scenery up in the mountains. Their lives are dominated by acre-feet and cubic feet per second, the measures of how much water in the river is available for agricultural, industrial and domestic use. What gets lost in the shuffle is that downstream part, past the spectacular parks and huge reservoirs. That part of the river in the long run might be the most important.

The Great Valley of California is one of the most productive landscapes on planet Earth. We subsumed most of it, 95%, for our own purposes, but the valley still supports a stunning variety of plant and animal life. In my own county alone, more than 300 bird species have been sighted at one time or another. Vast numbers of Arctic-breeding birds, Snow Geese, Sandhill Cranes, Cackling Geese, Ross's Geese, and White-fronted Geese still spend the winter in the small wildlife refuges that preserve a portion of the wetlands that once existed in the valley.

A Northern Flicker, a type of woodpecker, on a dead oak tree along the river trail.

Many of these facts are unknown to the children of our valley (and yes, their parents and grandparents too). Many of them live next to some of these arteries of life that flow past their towns, and the birds, insects and other animals lurk unseen just a few blocks from their homes. There is a huge need for nature education for these students, and the rivers are marvelous outdoor laboratories.

Foundations for a stairway that will provide access to the river. It's within walking distance of three schools.

So I'm excited by a few developments in the last few months. I've written a great deal about the Great Valley Museum on my campus in Modesto, but something else is happening right in my own backyard in Waterford. The small city has recognized the value of the beautiful river flowing nearby and is putting the finishing touches on a two-mile long river trail that will include interpretive signs and chances to see wildlife, as well as water-related recreation. An opening ceremony will take place on November 21.

A female Phainopepla. The males are pure black. This is the first time I've seen one around here.

I've been walking the river trail for months now, watching the progress. Today's walk was unusually rich in wildlife discoveries. Standing under a native Elderberry I saw a half dozen bird species, including Yellow-rumped Warblers, Vireos, a Black Phoebe, a Scrub Jay, a finch, and for the first time for me, a Phainopepla! I've seen them in the deserts east of the Sierra Nevada, but never here at home.

A Black Phoebe, a species of tyrant flycatcher.

It's been a tough year for wildlife as we suffer through another year of unprecedented drought. The rivers have been low and choked with invasive Hyacinth, but they've continued to flow, providing life for the birds, the mammals, and the fish, including the salmon. Until the San Joaquin River is rehabilitated, the Tuolumne River is pretty much the southernmost river providing at least some refuge to the endangered Chinook Salmon. The low flows have contributed to declines in their population. But life persists. And soon our children will have better opportunities to see the birds and other animals in their native habitats.

A Yellow-rumped Warbler

It's so easy to live in our insulated homes and ignore that we are part of a larger ecosystem. Preservation of our river and valley environments provides us an opportunity to learn more about our place in the greater scheme of things. Next time you are heading up to Yosemite National Park, or to the reservoir for some recreation, stop in Waterford and check out our modest effort to explain the value of the lower Tuolumne River. It's not Yosemite, but it has its own separate kind of beauty.

I'm not sure what kind this one is, but others I've seen around this shrub have been Black-chinned Hummingbirds.

About Me

I am a teacher of geology at Modesto Junior College and former president of the National Association of Geoscience Teachers, Far Western Section. I have led field trips all over the western United States, and a few excursions overseas, but my homebase is the Sierra Nevada, the Great Valley, and the Coast Ranges of California.

Ask Geotripper

Is there something about geology that you are curious about? Do you have questions about the scientific aspects of political controversies? I can try to provide a scientist's perspective. Your questions and possible answers could be a springboard to a blog discussion, or they can be private. Anonymity is always assumed. Contact Geotripper at hayesg (at) mjc.edu.

Blooks, Boogers and Bleries

Here are some of the series I've produced for the Geotripper Blog:

The Other California: what to see when you've seen all the really famous places in the Golden State (in progress).Into the Great Unknown: A rafting journey down the Colorado River through the Grand Canyon. The most incredible adventure of my life (so far)!

The Hawai'i That Was: An exploration of the geology, natural history, and anthropology of the most isolated lands on the planet. It's a lot more than beaches, shopping, and palm trees!